Wells are drilled to extract oil and gas from subterranean reservoirs. Oil and gas typically enter the well from the producing reservoir through perforations in the well casing. Initially, the reservoir pressure may be sufficient to overcome the force of gravity and force oil and gas out of the well. As the reservoir pressure decreases, however, fluids may accumulate at the bottom of the wellbore and it may become necessary to employ artificial lift systems to harvest the oil and gas. Examples of artificial lift systems include surface-mounted sucker rod pumps, electrical submersible pumps, plunger-lifts and gas-lift systems.
Gas lift systems involve injecting gas through the tubing-casing annulus of the well to aerate the accumulated fluid at the bottom of the well. The injected gas aerates the fluid to reduce its density and the reservoir pressure is then able to lift the oil column and forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment.
Generally, the use of density-reducing foam in conjunction with gas lift systems has proven to be an efficient and cost effective method for improving the recovery of petroleum products from the wellbore. However, many current foam generators require that the foam be generated at the surface and then pumped down into the wellbore. Alternatively, foam generation equipment must be installed in the equipment string in the well, which requires shutting-in the well while the new equipment is installed and removed. There is therefore a need for an improved foam generator that can generate foam in-situ in the well-bore and that can be selectively activated without interrupting the production of oil and gas.